The present invention relates to gas turbine engines having a dual wall cooling liner, and more particularly to an exhaust duct cooling liner for a non-axi symmetric cooling liner.
In order to improve gas turbine engine operation and performance, the usage of exhaust duct cooling air is carefully rationed. The cooling air is generally extracted from the engine fan flow, this extracted cooling air is a penalty to the overall performance of the engine. In current gas turbine engine exhaust ducts, a liner is disposed between the engine's working medium (exhaust gas path) and the engine outer casing or vehicle exhaust duct. Cooling air typically extracted from the engine's compressor is flowed within the liner and duct then discharged over the nozzle located at the end of the exhaust duct. A relatively significant quantity of cooling air is required to properly cool the exhaust duct and to maintain a positive pressure within the cooling liner while being subjected to large core pressure gradients at various operating conditions.
Advanced gas turbine engine exhaust systems are tending toward non axi-symmetric shapes. These shapes advantageously facilitate low observability and vectoring capabilities but generate a non-uniform core pressure field on the cooling liner. As the liner is film cooled, the non-uniform core pressure distribution posses a relatively significant challenge in the maintenance of a minimum pressure ratio between the local maximum core pressure and the cooling airflow supply pressure so as to prevent the high temperature core gases from being ingested into the liner system. If the cooling supply pressure cannot be spatially adjusted to match the non-uniform core pressure field, a greater quantity of cooling air may be required to achieve the minimum cooling to core pressure ratio than would otherwise be necessary to cool the liner as the cooling airflow is typically baselined for the most adverse pressure gradient during the most adverse operating condition. The non axi-symmetric and non-linear shaped exhaust duct further complicates the consistent preservation of a positive pressure gradient.
Current cooling liners, although effective, are still somewhat lacking in the compartmentalization fidelity necessary to maintain a positive pressure gradient along the entire length of a non axi-symmetric and non-linear cooling liners. Such lack of fidelity results in a relatively inefficient usage of cooling air, which may at least partially, penalizes engine performance.
Accordingly, it is desirable to provide effective cooling of a non axi-symmetric exhaust duct which maintains a positive pressure along the cooling liner while subjected to a large core pressure gradient, yet efficiently utilizes the cooling airflow.